Map One to two association - jpa

Question

I want to map exactly two players to one team with a bidirectional association. For that i use two attributes at the team Entity (for the player) and one attribute at the player (for the team).
Team class:
#Entity
public class Team implements Serializable {
#Id
private int id;
#OneToOne(mappedBy = "name")
private Player player1;
#OneToOne(mappedBy = "name")
private Player player2;
...
}
Player class:
#Entity
public class Player implements Serializable {
#Id
private String name;
#OneToOne
#JoinColumn(name = "TEAM_ID")
private Team team;
...
}
When deploying i got following error:
Internal Exception: Exception [EclipseLink-7244] (Eclipse Persistence Services - 2.7.4.v20190115-ad5b7c6b2a): org.eclipse.persistence.exceptions.ValidationException
Exception Description: An incompatible mapping has been encountered between [class [...].data.entities.Team] and [class [...].data.entities.Player]. This usually occurs when the cardinality of a mapping does not correspond with the cardinality of its backpointer.
What is the correct way to map a 1:2 association in JPA?

Answer 1

I think there is problem in database releations:
Player and Team has two OneToMany Realation(one player can b in many team)
You Should changed to this:
Team class:
#Entity
public class Team implements Serializable {
#Id
private int id;
#OneToMany
#JoinColumn(name = "player_id_1")
private Player player1;
#OneToMany
#JoinColumn(name = "player_id_2")
private Player player2;
...
}
Player class:
#Entity
public class Player implements Serializable {
#Id
private String name;
#ManyToOne(mappedBy = "player1")
private Set<Team> teamPlayer1;
#ManyToOne(mappedBy = "player2")
private Set<Team> teamPlayer2;
...
}

Answer 2

You have described a OneToMany/ManyToOne relationship in the database, but without any ordering. Try mapping it as such and using the position within the list to define the relationship - you can limit it to allowing only collections of size 2 in code or at the database yourself if you need.
#Entity
public class Team implements Serializable {
#Id
private int id;
#OneToMany(mappedBy = "team")
#OrderColumn
private List<Player> players;
...
}
#Entity
public class Player implements Serializable {
#Id
private String name;
#OneToOne
#JoinColumn(name = "TEAM_ID")
private Team team;
...
}
The addition of the #OrderColumn will create a column in the Player table to track their position within the team list.
This then allows you to always assume player1 will be in the first position, while player2 is second in the list and so can write get/setPlayer1 and get/setPlayer2 methods appropriately - just take care to handle empty lists and null values.